Aircraft reference program generator

ABSTRACT

An analog position transducer connected to an aircraft flap generates a linear voltage representing flap position. Separate switching stages are responsive to different potential levels of the linear voltage to produce separate output waveforms which are summed by an operational amplifier for each reference program which is to be generated. The disclosed reference programs correlate desired angle of attack to flap position for an aircraft approach program and a climbout program.

United States Patent 1 3,636,32 1

Kirschner [4 1 Jan. 18, 1972 [54] AIRCRAFT REFERENCE PROGRAM PrimaryExaminer-Malcolm A. Morrison GENERATOR 7 Robert K. Kirschner, Bellevue,Wash.

Assistant Examiner-R. Stephen Dildine, Jr. Attorney-Hofgren, Wegner,Allen, Stellman & McCord BIAS I32 [72] Inventor: [73] Assignee:Sundstrand Data Control, Inc. [57] ABSTRACT v An analog positiontransducer connected to an aircraft flap [22] filed 1969 generates alinear voltage representing flap position. Separate [21] App]. No.:883,852 switching stages are responsive to different potential levels ofthe linear voltage to produce separate output waveforms which are summedby an operational amplifier for each [52] 135/1503 reference programwhich is to be generated. The disclosed G06 1, 2 6 78 reference programscorrelate desired angle of attack to flap 7 93 5 4 2 position for anaircraft approach program and a climbout pro- [56] References Cited 12Claims 2 Drawing Figures UNITED STATES PATENTS 3,241,792 3/1966l-lattendorf ..244/77 D IC 1 vous o flu o5|o 20 26 FLAP I +|ovTRANSDUCER +|3v +2ev +|ov +1cv +2av 10v mv & I 94 22 i 2/ 80 b i HM +|ovos|o 20' so o5|o 20 so /4 Z cums our 6/ VOLTS- lf PROGRAM FLAP ANGLEFLAP ANGLE to provide an input to an automatic control system or a pilotdisplay. For example, a reference program generator may correlate flapposition with desired angle of attack. Often, separate programs aregenerated for different flight routines, such as for climbout andapproach. j

Flap position with respect to an airfoil is usually constrained tocertain discrete values, such as etc. During the transition periodbetween discrete flap positions, the output command from prior referencegenerators experience a discontinuity or jump which requires specialsmoothing circuitry to prevent undesired system response. In addition toadding to the complexity of the reference generator, the smoothingcircuitry does not produce a reference program which faithfullyrepresents flap position during flap transition periods.

In a typical prior flap position transducer, mechanical switches arelinked to the flap for actuation during each transition of the flapbetween discrete flap positions. When a conventional reference programgenerator is connected to the mechanical switches, the resulting programoutput has undesirable stepped transitions during the transitionperiods. Between the transition periods, however, a flat plateau regionis formed which is desirable in that there is a lack of ambiguity in theflap signal even when there is minor mislocations of the flap within theflap position tolerance band. It would be desirable to retain thegeneration of flat plateau regions while eliminating the disadvantagesof prior systems. For example, the mechanical switches forming a flapposition transducer have a low reliability and undesirable weight andcost when the switches are located in an aircraft wing in order to sensetrue flap position. Also, smoothing circuitry produces a referenceprogram which does not trulyrepresent flap position between discreteposition values.

In accordance with the present invention, an improved reference programgenerator is disclosed which retains the advantages of prior systems,while eliminating the disadvantages, An analog linear positiontransducer is connected to a flap in order to provide a continuous flapposition signal with smoothly varying values during flap changes. Inplace of prior reference program generators, an electronic functiongenerator is used which provides smooth analog transitions in thereference program during flap changes. In addition, the functiongenerator has dwell or plateau regions for each flap position, which canbe tailored to a specific aircraft to accommodate variations in flapposition accuracy. The present invention can generate as many separatereference programs as required, as for approach and for climbout,without requiring a corresponding increase in the number of partsforming the generator.

While the applicants reference program generator is illustrativelydisclosed for forming an angle of attack program for discrete flappositions, the program generator is equally usable for generating anyreference program correlating the position of a control surface of anaircraft to a desired aircraft flight condition. Many control surfacesother than flaps may be used with the reference generator, includingmovable wing surfaces such as used in STOL and VTOL aircraft, as well asother control surfaces.

One feature of this invention is the provision of an aircraft referenceprogram generator for correlating a desired aircraft flight condition tothe position of a controlsurface connected to an analog linear positiontransducer.

Another feature of this invention is the provision of an aircraftreference program generator having a minimum number of components forgenerating plural reference programs, each of which is tailored to adifferent flight routine.

Further features and advantages of the invention will be apparent fromthe following specification, and from the drawings, in which:

FIGS. 1A, 1B and 1C show three forms of reference programs generated bydifferent types of reference program generators; and

FIG. 2 is a partly block and partly schematic diagram of the invention.I .1

While an illustrative embodiment of the invention is shown in thedrawings and will be described in detail herein, the invention issusceptible of embodiment in many different forms and it should beunderstood that the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedto limit the invention to the embodimentillustrated.

In FIG. 1, three reference programs correlating angle of attach to flapposition are illustrated in order to illustrate how the applicant'sgenerator eliminates the disadvantages of prior generators whileretaining the advantages thereof. In all three parts of the diagram, thesame basic program' has been generated to provide specific angle ofattack values for specific discrete flap positions of 0, 5?, 10, 20 and30". For convenience, the intersection of the discrete flap positionvalues with the generated program curve are indicated by small circles.

FIG. IA illustrates a reference program generated by a typical priorreference generator usinga mechanical switch flap position transducer.For each discrete flap position, a flat plateau region 10 of the programcurve desirably provides a nonambiguous value of desired angle ofattack. However, during the period of flap transition, the generatedcurve has an undesirable perpendicular discontinuity region 11 while thecurve jumps between adjacent plateau regions 10. The regions 11 havesubstantially comers at both the start and termination of the transitiontime. The resulting sharp discontinuities require special smoothingcircuitry to avoid a discontinuity in a system output command.

The reference program generated by the preferred form of the presentinvention is illustrated in FIG. 1C. The curve has dwell or plateauregions 14 which, likethe regions 10 in FIG. 1A, provide nonambiguousvalues of angle of attack. Unlike FIG. 1A, the transition regions 15,between the plateaus I4, have a smooth analog ramp or skewed shape inwhich the corners or points of discontinuity are not perpendicular, butrather have an angle other than 90. The skewed transition regions l5desirably provide an unambiguous angle of attack signal for each valueof flap position, including flap positions between discrete values.

In FIG. 2, a preferred form of the reference program generator isillustrated, which generates the reference program shown in FIG. 1C. Atransducer 20 is connected to a movable control surface in an aircraft,such as a flap 21 movable with respect to an airfoil 22. Transducer 20may be any suitable position responsive transducer having an analogoutput with a continuously variable quantity representing the actualposition of the connected movable element. A suitable transducer 20would be one having a voltage output 25 such as illustrated by the chartin FIG. 2. The voltage output 25 smoothly and continuously varies froml0 volts DC3 at 0 flap position, to +10 volts DC at 30 flap position.This voltage is coupled over a transducer output line 26 to a switchingmeans with four stages 30, 31, 32, and 33. The number of stages is equalto the number of transitions between discrete flap positions. Sincethere are five discrete flap positions, namely 0, 5, 10, 20 and 30,there are four transition regions and hence four stages 30-33.

Each switching stage contains a controllable conduction device, such asNPN-transistor 40, connected to form a switching circuit having anoutput voltage on an output line 42. The voltage outputs for each of theindividual stages 30 to 33 are illustrated by the curves 50 t0 53,respectively. Each stage switches ata different voltage level fromtransducer output line 26, thereby producing four separate switchingwaveforms.

By way of example, it will be assumed that a particular aircraft typerequires that a separate climbout reference program and a separateapproach reference program be generated with values tailored to theflight characteristics of that aircraft. For this situation, a firstsummer 60 combines the separate switching waveforms 50-53.from stages30-33 in a selected weighted manner to generate, on an output line 61, aclimbout program. A second summer 64 combines the switching waveforms50-53 from the stages 30-33 with different weights in order. to produce,on an output line 65, an approach program. As many additional summersmay be provided as are necessary for the number of separate programs tobe generated; however, only a single set of switching stages 30-33 arenecessary. The reference programs on lines 61 and 65 may be connected ina conventional manner with a known comparison circuit having anotherinput representing actual angle of attack. The difference between thereference angle of attack and the actual angle of attach may be used togenerate an error signal input to either an automatic speed/altitudecontrol system and/or a pilot display, as is conventional.

Considering the circuit of FIG. 2 in more detail, switching stages 30and 31 use identical circuits with different values of components inorder to produce the separate switching waveforms 50 and 51. Only thestage 30 will be explained in detail, it being understood that the stage31 operates in a similar manner.

To connect transistor 40 in stage 30 to transducer output line 26, apair of voltage-divider resistors 70 and 71 are connected in seriesbetween line 26 and a source of +10 volts DC potential. The junctionbetween resistors 70 and 71 is connected through a diode 73 to the baseof transistor 40. The emitter of transistor 40 is connected directly toa source of reference potential or ground 75. In the circuit, allpositive and negative DC-potentials are referenced to ground 75. Anyconventional DC-power supply may be used to produce the output voltagesindicated in the drawing.

The collector of transistor 40 is connected through a resistor 77 to +28volts DC and also through a diode 79 to +10 volts DC. A second diode 80,poled in the same direction as diode 79, is connected between thecollector of transistor 40 and output line 42 for stage 30. Thecollector of the transistor is also connected through a feedbackresistor 82 to the base electrode, and the junction between resistor 82and the base electrode is connected through a biasing resistor 84 to +10volts DC.

The operation of stage 30 may be understood by refening to the voltagecurve 50 which is generated on output line 42. Transistor 40 is biasedinto its nonconducting region for transducer voltages on line 26 morenegative than 9 volts or so. During this time, the junction betweenresistor 70 and 71 is at zero or a slight positive voltage, sufiicientto allow diode 73 to remain conductive by the current path from +10volts and resistor 84 to the anode of the diode.

As the voltage on line 26 rises above this switching point, as occurs ata point 90 on the voltage curve 50, diode 73 becomes nonconductive,unclamping the base electrode from its prior substantially groundpotential, causing transistor 40 to be driven into its conductingregion. The collector electrode, previously clamped at approximately +10volts (minus the voltage drop through the conduction diode 79), nowbegins to drop in potential as the collector to emitter resistance ofthe transistor forms a voltage divider with resistor 77. The diode 80passes the positive voltage at the collector electrode, producing thevoltage curve 50 on line 42.

Transistor 40 will continue to be driven more conductive until itreaches its saturation level which substantially clamps the collectorelectrode to ground potential, as corresponds to a point 92 on curve 50.The transition period between points 90 and 92 is located between thediscrete flap positions of and and the ramp-shaped voltage betweenpoints 90 and 92 is used to form the first transition period in thereference programs. Desirably, the ramp region between points 90 and 92has a lesser extent than the transducer voltage region from one discreteflap position to the next discrete flap position, in

order to form the plateau regions 14 which provide the unambiguousindication of discrete flap positions.

Stage 30 is compensated for temperature effects by the diode which ischosen to have the same temperature curve as diode 79. Thus, variationsin the voltage drop across the clamping diode 79 are compensated for bythe corresponding variations occurring in the voltage drop across diode80. The selection of the values of DC-supply potentials and the valuesof the resistors control the steady state levels of the curve 50 and thelocation of points and 92. For stage 30, the ramp between points 90 and92 is chosen to occur during the first transition period between thediscrete flap positions of 0 and 5. For stage 31, the voltage dividerresistors 70 and 71 are chosen to have different values so that the rampfor curve 51 occurs between the next discrete flap positions of 5 and10. Otherwise, the stage 31 operates in the same manner as stageSwitching stages 32 and 33 use a different circuit to form switchingvoltages 52 and 53, respectively, which voltages are generally inverseto those produced by stages 30 and 31. The circuits for stages 32 and 33are identical, with different component values being used to vary thepoint of switching. Only stage 32 will be explained in detail. v

A pair of voltage divider resistors and 101 are connected in seriesbetween transducer line 26 and l0 volts DC. The junction betweenresistor 100 and 101 isconnected through a diode 103 to the base oftransistor 40. The collector of the transistor is connected through aresistor 105 to +10 volts potential, while the base electrode isconnected through a biasing resistor 107 to the same +10 volts DC. Theemitter electrode is connected directly to line 42, and through anemitter resistor 109 to ground 75.

in operation, transistor 40 of stage 32 is nonconducting for flap anglesfrom 0 through 10, causing the voltage output curve 52 to besubstantially at ground potential. At a point 112 beyond the discrete 10flap position, the junction between resistors 100 and 101 becomespositive by an amount exceeding the required voltage drop across diode103 and the base-emitter junction of transistor 40. As a result, thevoltage at the base electrode becomes sufficiently positive to forwardbias transistor 40 and cause it to operate in its conductive region.This produces a ramp-shaped conduction curve which forces currentthrough the emitter resistor 109, producing a voltage drop which causesthe voltage on line 42 to rise positively. At a voltage point 115,transistor 40 is driven into its saturated conduction state, maintainingthereafter the steady state voltage output of approximately +l volts DC.

The ramp voltage between points 112 and 115 is chosen to fall betweenadjacent discrete values of flap position, for the same reason aspreviously explained for the ramp between points 90 and 92 of curve 50.The operation of stage 33 is substantially the same as that for stage32, except the resistance of resistors I00 and 101 are chosen so thatthe point at which its transistor 40 is first driven into conduction isdelayed sufficient so that the ramp falls between the discrete flappositions of 20 and 30 The stages 32 and 33 are temperature compensatedby the base input diode 103 which compensates for the base-to-emittervoltage drop across the conducting transistor 40.

Summers 60 and 64 individually add the voltage waveforms 50 through 53in order to form separate reference programs. Each summer has a similarcircuit, with different component values being used in order to weighteach input waveform differently in order to alter the plateau voltagelevels of the reference program generated thereby. Summer 60 will beexplained in detail. A plurality of resistors are individually connectedbetween each output line 42 of stages 30-33 and a common summingjunction122. To invert the voltage at junction 122, an operational amplifier hasits input connected to junction 122, and its output connected directlyto the output line 61. A feedback resistor 127 is connected between line61 and the input. The input of the operational amplifier is connectedthrough a resistor 130 to ground 75. To adjust the basic level of thereference program, a bias resistor 132 is connected between summingjunction 122 and a potential line 133 which carries a reference DC-biasvoltage.

Concerning the values of the components, the resistance value of eachresistor 120 is chosen so that its corresponding voltage curvecontributes the desired level of voltage to the reference program. Thesteady state regions of the voltage curves 50*53 form the plateauregions 14 in the final reference program. The ramp shaped transitionareas form the transition regions 15 in the final program. The overalllevel of the final reference program is controlled by selection of anappropriate value for bias resistor 132.

The resistors 120 for summer 64 have different values than the resistors120 for summer 60, in order to provide different weights to the voltagecurves 50 to 53 in order to form a different reference program output online 65. As illustrated, the values of resistors 120 of summer 60 werechosen to form on line 61 a climbout program while the values ofresistors 120 ofsummer 64 were chosen to form on line 65 an approachprogram. The output resistance of each of the stages 30-33 is madesufficient low, by the feed back resistor 82 and clamping diode 79 ofstages 30 and 31, and the low value of the emitter resistor 109 instages 32 and 33, so that adjustment of the resistors 120 for one summerdoes not significantly alter the reference program generated by theother summer. Thus, interacting resistor networks have been eliminated.

The program generator of FIG. 2 is the preferred form for implementingthe invention. In place of the illustrated program generator, aconventional resister divider diode function generator could beconnected to the analog transducer and still provide a reference programwith smoothly controlled values during flap changes. A reference programproduced by such a function generator would have the form illustrated inFIG. 18. While the smooth, continuous form of the program curveapproaches an idea program from the aerodynamic standpoint, variationsin the resting or discrete positions of the flaps cause undesirablesystem variations. it is preferred that each discrete flap position havea plateau region 14 associated therewith, which do not occur in the FIG.1B program. Also, separate diode function generators would have to beprovided for each program to be generated. For these reasons, thecircuit of FIG. 2 is preferred over a conventional function generatorconnected to an analog transducer.

1 claim:

1. In an aircraft having a control surface movable to differentpositions to control an aircraft flight condition, a reference programgenerator for generating a reference program correlating control surfaceposition to a desired aircraft flight condition, comprising:

transducer means associated with said control surface for generating ananalog signal having a continuously variable quantity representing theposition of said control surface; and

program means coupled to said transducer means for generating areference signal having points corresponding to discrete positions ofsaid control surface as represented by predetermined analog signalquantities, including transition means for causing said reference signalto have a nonperpendicular skewed transition region between said points.

2. The reference program generator of claim 1 wherein said transitionmeans causes said reference signal to have substantially flat plateauregions about each of a plurality of said points, the nonperpendicularskewed transition regions occuring between plateau regions.

3. The reference program generator of claim 2 wherein said transitionmeans causes said points to be located in the midsections of saidsubstantially flat plateau regions.

4. The reference program generator of claim 1 wherein said transitionmeans includes a plurality of stages each including switching meansresponsive to a different predetermined analog signal quantity forgenerating a switching signal, and wherein said program means furtherincludes means for combinin said switchingsignals to form said referencesi nal.

5. e reference program generator of claim wherein each switching meansincludes a controllable device for varying the switching signal levelwhen actuated, and bias means connecting said controllable devices tosaid transducer means to actuate the device associated with a givenswitching means when the analog signal exceeds the predeterminedquantity for that switching means. 7

6. The reference program generator of claim 5 wherein said controllabledevices comprise transistors having a variable conduction region, saidbias means operating said transistors in said conduction region when thetransistors are actuated.

7. The reference program generator of claim 5 wherein said combiningmeans includes a plurality of impedance means each coupled to adifferent one of said plurality of stages, and circuit means connectedto. said impedance means to sum the switching signals in order to formsaid reference signal.

8. The reference program generator of claim 7 wherein each impedancemeans comprises a resistor, said circuit means comprises a commonsumming point for said resistors and amplifying means connected to saidsumming point for generating said reference signal.

9. in an aircraft having a control surface movable to differentpositions to control an aircraft flight condition, a reference programgenerator for generating a reference program correlating control surfaceposition to a desired aircraft flight condition, comprising:

transducer means associated with said control surface for generating asignal representing the positions of said control surface;

generating means coupled to said transducer means for generating aplurality of separate signals, each signal having a discontinuity at adifferent point; and

a plurality of program means each connected to said generating means forcombining differently the separate signals to generate a plurality ofdifferent reference program signals.

10. The reference program generator of claim 9 wherein each programmeans includes a summing point and a plurality of impedance meanscoupling the separate signals from said generating means to the summingpoint, at least one of the impedance means of each program means havinga different impedance value than a corresponding impedance means of theother program means in order to sum differently the separate signals.

11. The reference program generator of claim 9 wherein said transducermeans generates an analog signal having a continuously variable quantityrepresenting the position of said control surface, and said generatingmeans comprises a plurality of stages coupled to said transducer meansand each including switching means responsive to a differentpredetermined analog signal quantity to form the signal discontinuitiesin the separate signals.

12. The reference program generator of claim 11 wherein said separatesignals each have a pair of discontinuities with a variable ramp regiontherebetween, said program means being responsive to the ramp regions tofonn nonperpendicular skewed transitions in said reference programsignals.

1. In an aircraft having a control surface movable to differentpositions to control an aircraft flight condition, a reference programgenerator for generating a reference program correlating control surfaceposition to a desired aircraft flight condition, comprising: transducermeans associated with said control surface for generating an analogsignal having a continuously variable quantity representing the positionof said control surface; and program means coupled to said transducermeans for generating a reference signal having points corresponding todiscrete positions of said control surface as represented bypredetermined analog signal quantities, including transition means forcausing said reference signal to have a nonperpendicular skewedtransition region between said points.
 2. The reference programgenerator of claim 1 wherein said transition means causes said referencesignal to have substantially flat plateau regions about each of aplurality of said points, the nonperpendicular skewed transition regionsoccuring between plateau regions.
 3. The reference program generator ofclaim 2 wherein said transition means causes said points to be locatedin the midsections of said substantially flat plateau regions.
 4. Thereference program generator of claim 1 wherein said transition meansincludes a plurality of stages each including switching means responsiveto a different predetermined analog signal quantity for generating aswitching signal, and wherein said program means further includes meansfor combining said switching signals to form said reference signal. 5.The reference program generator of claim 4 wherein each switching meansincludes a controllable device for varying the switching signal levelwhen actuated, and bias means connecting said controllable devices tosaid transducer means to actuate the device associated with a givenswitching means when the analog signal exceeds the predeterminedquantity for that switching means.
 6. The reference program generator ofclaim 5 wherein said controllable devices comprise transistors having avariable conduction region, said bias means operating said transistorsin said conduction region when the transistors are actuated.
 7. Thereference program generator of claim 5 wherein said combining meansincludes a plurality of impedance means each coupled to a different oneof said plurality of stages, and circuit means connected to saidimpedance means to sum the switching signals in order to form saidreference signal.
 8. The reference program generator of claim 7 whereineach impedance means comprises a resistor, said circuit means comprisesa common summing point for said resistors and amplifying means connectedto said summing point for generating said reference signal.
 9. In anaircraft having a control surface movable to different positions tocontrol an aircraft flight condition, a reference program generator forgenerating a reference program correlating control surfAce position to adesired aircraft flight condition, comprising: transducer meansassociated with said control surface for generating a signalrepresenting the positions of said control surface; generating meanscoupled to said transducer means for generating a plurality of separatesignals, each signal having a discontinuity at a different point; and aplurality of program means each connected to said generating means forcombining differently the separate signals to generate a plurality ofdifferent reference program signals.
 10. The reference program generatorof claim 9 wherein each program means includes a summing point and aplurality of impedance means coupling the separate signals from saidgenerating means to the summing point, at least one of the impedancemeans of each program means having a different impedance value than acorresponding impedance means of the other program means in order to sumdifferently the separate signals.
 11. The reference program generator ofclaim 9 wherein said transducer means generates an analog signal havinga continuously variable quantity representing the position of saidcontrol surface, and said generating means comprises a plurality ofstages coupled to said transducer means and each including switchingmeans responsive to a different predetermined analog signal quantity toform the signal discontinuities in the separate signals.
 12. Thereference program generator of claim 11 wherein said separate signalseach have a pair of discontinuities with a variable ramp regiontherebetween, said program means being responsive to the ramp regions toform nonperpendicular skewed transitions in said reference programsignals.